1. Field of the Invention
Aspects of the present invention relate to a surface treated anode, and a lithium battery using the same.
2. Description of the Related Art
Various conventional techniques, proposing the use of lithium metals as anode active materials for lithium batteries, have been suggested. However, when lithium metals are used in lithium batteries, short circuits may occur, due to lithium dendrite formation, which can cause explosions. Thus, carbonaceous active materials have been widely used as anode materials, instead of lithium metals. Examples of such carbonaceous active materials include: crystalline carbon, such as, natural graphite and artificial graphite; and amorphous carbon, such as, soft carbon and hard carbon. However, although amorphous carbon has a high capacity, many of its charge/discharge reactions are irreversible. Since the theoretical capacity of crystalline carbon (including graphite) is relatively high, i.e., 372 mAh/g, crystalline carbon is widely used as an anode active material. Although the theoretical capacity of such graphite or carbon-based active materials (approximately 380 mAh/g) is relatively high, it is not high enough for future higher capacity lithium batteries.
To address these problems, research on metal-based and metalloid-based, anode active materials has been actively conducted. For example, research on lithium batteries using metals or metalloids, such as, aluminum, germanium, silicon, tin, zinc, lead, etc., as the anode active material, has been conducted. Such materials are known to have large capacities, high energy densities, and good insertion/extraction capabilities, as compared to carbon-based anode active materials. Thus, lithium batteries having large capacities and high energy densities can be prepared using these materials. For example, pure silicon is known to have a high theoretical capacity of 4017 mAh/g.
However, such materials have shorter life cycles than carbon-based materials, and thus, cannot be put to practical use. When inorganic particles, such as, silicon or tin are used as the anode active material, the volume of inorganic particles changes considerably during charge/discharge cycles. This may result in the degradation of an electronic conduction network between the active material particles, or may result in the detachment of an anode active material from an anode current collector. That is, the volume of an inorganic material, such as, silicon or tin, increases by about 300 to 400%, due to alloying with lithium during charging. The volume decreases during discharging, due to the extraction of lithium. Therefore, after repeated charge/discharge cycles, spaces may be generated between the active material particles, and electrical insulation may occur, thereby rapidly lowering the life cycle characteristics of these materials, and causing serious problems when using these materials in lithium batteries.
Recently, various attempts have been made to develop new active materials for secondary batteries, having increased theoretical capacities. One such attempt includes the use of high-capacity, composite, anode active materials, for example, silicon (Si)-carbon (C), or tin (Sn)-carbon (C). However, there may be several disadvantages in using such materials, such as, severe electrochemical irreversibility during charging and discharging. This may be caused by increases in the defects and the specific surface area of carbon, during a compounding process. In addition, the charge/discharge efficiency is lowered, due to weakened bonds between active material particles, which may be caused by the extreme expansion and contraction of the active materials.